Sized carbon fibers

ABSTRACT

Carbon fibers are coated with a sizing composition comprising a polyglycidyl ether, cycloaliphatic polyepoxide or their mixtures. Preferred sizes are mixtures of a liquid diglycidyl ether of bisphenol A and a solid diglycidyl ether of bisphenol A.

United States Patent [1 1 Weldy Oct. 21, 1975 1 SIZED CARBON FIBERS [75]Inventor: Winfred E. Weldy, Wilmington, Del.

[73] Assignee: Hercules Incorporated, Wilmington,

Del.

[22] Filed: Oct. 1, 1973 [21] Appl. No.: 402,493

139.5 CQ,117/228, 121, DIG. 11; 260/37 EP, 47 EP, 830 TW; 423/447, 460;8/115.6, 140; 161/176 [56] References Cited UNITED STATES PATENTS2,735,829 2/1956 Wiles et a1 260/830 TW 4/1959 Reid] et al. 117/161 ZB8/1963 Wayne 260/830 TW 3,298,859 1/1967 Wong et al. 117/126 3,441,5224/1969 Soldatos et al. 117/161 ZB 3,512,919 5/1970 Cappuccio et al..8/115 6 3,660,140 5/1972 Scola et a1. 117/161 ZB 3,806,489 4/1974 Rieuxet a1 260/38 3,837,904 9/1974 Hill 117/139-.5 A

3,839,072 10/1974 Kearsey 8/115.6 3,844,822 10/1974 Boss et a1 117/161 ZPrimary Examiner-Michael Sofocleous Attorney, Agent, or Firm-Edith A.Rice; Michael B. Keehan [5 7 ABSTRACT Carbon fibers are coated with asizing composition comprising a polyglycidyl ether, cycloaliphaticpolyelpoxide or their mixtures. Preferred sizes are mixtures of a liquiddiglycidyl ether of bisphenol A and a solid diglycidyl ether ofbisphenol A.

4 Claims, 1 Drawing Figure US. Patent 0c:. 21,1975 3,914,504

SIZED CARBON FIBERS This invention relates to protective sizingcompositions for carbon fibers and in particular to protective sizingcompositions for'carbon fibers based on certain epoxy compounds. 1 t IThe term carbon fibers is used in this application in its generic senseand includes both graphite fibers and amorphous carbon fibers. Graphitefibers are-defined herein as fibers whichconsist essentially of carbonand have a predominate X-ray diffraction'pattern,characteristic ofgraphite. Amorphous carbon fibers, on the other hand, aredefined-asfibers inwhich the bulk of the fiber weight can be attributedto carbon and which exhibit an essentially amorphous X-ray diffractionpattern. Carbon fibers can be prepared ,by known process from polymericfibrous materialssuch as polyacrylonitrile, polyvinyl alcohol, pitch,natural and regenerated cellulose, which processes include the steps ofcarbonizing or graphitizingthe fibers.

Carbon fibers are generally fragile and subject to abrasion duringhandling. It has now been discovered that sizing compositions based oncertain epoxy compounds protect carbon fibers against suchv damage. Whencarbon fibers are to be used in preparing composite structures withresin matrixsystems they are frequently subjected to a surfacepretreatment to improve the adhesion between the carbon fibers and theresin matrix. The fiber surface. is usually oxidized in such apretreatment, for example by reaction with an oxidizing'agent.Alternatively, the carbon fiber can be oxidiz ed by electrolytictreatment. using an electrolyte which will generate nascent oxygen atthe, surface of the carbon fiber during the electrolysis process. Thesizing compositions of this invention do not detract from the adhesionimprovement of such surface treated fibers. v

In accordance with this inventionthere is provided carbon fibers coatedwith a sizing composition comprising lan epoxy compound, selected fromthe group consisting of polyglycidyl ethers, cycloaliphatic polyepoxidesand mixtures thereof. The sized carbon fibers are compatible with epoxyresin matrix systems used to prepare composite structures. The size canbe applied to untreated or surface pretreated carbon fibers to protectthem against abrasion damage.

Polyglycidyl ethers which can be used,-in accordance with thisinvention, as a protective size for carbon fibers include diglycidylethers, triglycidyl ethers, tetraglycidyl ethers and higher polyglycidylethers. Mixtures of any of the polyglycidyl ethers can also be used.

Illustrative diglycidyl ethers that can be employed include diglycidylether; diglycidyl ether of 1,3- butanediol; 2,6-diglycidyl phenylglycidyl ether; 1,8- bis(2,3-epoxypropoxy)octane;l,3-bis(2,3-epoxypropoxy)benzene; l,4-bis( 2,3-epoxypropoxy)benzene;l,3-bis(4,5-epoxypentoxy)-5-chlorobenzene; 4,4bis(2,3-epoxypropoxy)diphenyl ether; 2,2-bis(2,3-epoxypropoxyphenyl)methane; and 2,2-bis[p-(2,3- epoxypropoxy)phenyl]propane, i.e., the diglycidyl ether of bisphenol A.

Illustrative triglycidyl ethers that can be employed include triglycidylethers such as the triglycidyl ethers of trihydric alcohols such asglycerol, l, l,l-tri(hydroxymethyl)propane, 1,2,6-hexanetriol and thehigher alcohols; and the triglycidyl ethers of trihydric phenols, suchas phloroglucinol, the trihydroxydiphenyl methanes and propanes, thetrihydroxyaminophenols, the trisphenols;2,2[2,4,4'-tris(epoxypropoxy)diphenyl]- propane; l, 1 -bis(glycidyloxymethyl )-3 ,4-epoxycyclohexane; and N,N,Otris(epoxypropyl)p-aminophenol.

Illustrative tetraand higher polyglycidyl ethers that can be employedinclude tetraglycidyl ether of p,p'diaminodiphenylmethane and epoxidizednovolac compounds.

Cycloaliphatic polyepoxides which can be used to provide a protectivesize on carbon fibers in accordance with this invention includebis-2,3-epoxycyclopentyl ether; I,4-bis(2,3-epoxypropoxy)cyclohexane;l,4-bis(3,4-epoxybutoxy)-2-chlorocyclohexane; thedi(epoxycyclohexanecarboxylates) of aliphatic diols; the oxyalkyleneglycol epoxycyclohexanecarboxylates; the epoxycyclohexylalkylepoxycyclohexanecarboxylates; epoxycyclohexylalkyl dicarboxylates;epoxycyclohexylalkyl phenylenedicarboxylates; bis(3,4-epoxy-6-methylcyclohexylmethyl) diethylene glycol ether; dicyclopentadienedioxide; bis(2,3-epoxycyclopentyl) etheryglycidyl 2,3-epoxycyclopentylether; 2,3-epox ycyclopentyl 2-methylglycidyl ether; cycloaliphatictriepoxides; also tetraand higher homologues which contain more thanthree epoxy groups per molecule. Mixtures of the cycloaliphaticpolyepoxides can also be employed.

. Illustrative of the di(epoxycyclohexanecarboxylates) of aliphaticdiols which can be employed include thebis(3,4-epoxycyclohexanecarboxylate) of l,5-pentanediol, 3,-methyl-l,S-pentanediol, 2-methoxymethyl+ 2,4-dimethyl-l,S-pentanediol, ethyleneglycol, 2,2- diethyl-l,3-propanediol, l,6-hexanediol and 2-butene-1,4-diol. g a

. Illustrative of the oxyalkylene glycol epoxycyclohexanecarboxylateswhich can be employed include bis(2- ethylhexyl-4,5-epoxycyclohexane-l,2-dicarboxylate) of dipropylene glycol,bis(3,4-epoxy-6-methylcyclohexanecarboxylate) of diethylene glycol andbis(3,4-epoxycyclohexanecarboxylate) of triethylene glycol.

Illustrative of the epoxycyclohexylalkyl epoxycyclohexanecarboxylateswhich can be employed include 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-l-methylcyclohexylrnethyl 3,4epoxy-l-methylcyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl 3,4-epoxy-2-methylcyclohexanecarboxylate,3,4-epoxy-6-methylcyclohexylmethyl3,4-epoxy-6-methylcyclohexanecarboxylate, (1-chloro-3,4-epoxycyclohexan-1-yl) methyl l-chloro- 3,4-epoxycyclohexanecarboxylate, l-bromo-3 ,4- epoxycyclohexan-l-yl)methyl l-bromo-3,4-epoxycyclohexanecarboxylate) and(l-chloro-2-methyl-4,5- epoxycyclohexan-l-yl) methyll-chloro-2-methyl-4,5- epoxycyclohexanecarboxylate.

Illustrative of the epoxycyclohexylalkyl dicarboxylates which can beemployed include bis(3,4-epoxycyclohexylmethyl) pimelate and oxalate andbis(3,4- epoxy-6-methylcyclohexylmethyl) maleate, succinate, sebacateand adipate.

Illustrative of the epoxycyclohexylalkyl phenylenedicarboxylates whichcan be employed include bis(3,4- epoxycyclohexylmethyl) terephthalateand bis(3,4- epoxy--methylcyclohexylmethyl) terephthalate.

Illustrative cycloaliphatic triepoxides which can be I employed includetris(3,4-epoxycyclohexanecarboxylate) of I,l,l-trimethylol propane; andtris(3,4-epoxycyclohexanecarboxylate) of 1,2,3-propanetriol.

The sizing composition can be applied to the fiber in a suitable solventto control the amount of size coated onto the fiber. However, the sizingcomposition can be applied directly, if desired. The concentration ofthe size in the solvent is usually in the range of from about 0.1 toabout 10.0% by weight based on the total weight of the solution and ispreferably from about 0.5 to about 2.0%. Examples of suitable solventsare polar solvents such as the halogenated hydrocarbons, for example,methylene chloride and ethylene dichloride; diacetone alcohol, ketonesand esters. If desired, the sizing composition may also contain alubricant. The lubricant serves to permit more even distribution of .thesize on the fiber and aids in more effective wetting of the fiber.Preferred lubricants are fatty acids, amides and esters. Otheradditives, such as coupling agents can also be added to the sizesolution.

The sizing compositions can be applied to the fibers by known methods,for example, by drawing the fibers through a bath containing the size orby spraying the size onto the fibers. The drawing illustrates apreferred arrangement for sizing carbon fibers. 1n the drawing, a carbonfiber strand 2 is drawn from supply reel 4 and passed into a tube 6. Thearrows indicate the direction the carbon fiber strand 2 travels. Thetube 6 is heated by hot air forced through the inlet tube 8 from asuitable source, such as an electric heat gun. The temperature of thehot air is sufficient to heat the tube to above the evaporationtemperature of the solvent. The fiber is passed along the tube and downthrough an opening 9 inthe bottom of the tube 6 and into the sizing bath10. The fiber-is directed down into the bath 10, through the bath andback through opening 9 into heated tube 6 by guide rollers 12, 14 and16. The fiber is passed through the heated tube to evaporate the solventand wound on a conventional take-up roll 18. The amount of size coatedonto the fiber is from about-0.4 to about 5.0%, by weight based on theweight of the fiber, preferably from about 0.9 to about 1.6%. The amountof size on the fiber is determined by weighing a given length of sizedfiber, then dissolving the size from the fiber using a solvent for thesize, drying the fiber and then reweighing the unsized fiber. From thedifference in the weights the percentage of size on the fiber, based onthe weight of the fiber, is calculated.

Carbon fibers sized with the epoxy compound sizing compositions of thisinvention can be used to prepare fiber reinforced composite structures.Any of the known methods for preparing such composites can be employed.For example, carbon fibers can be used to prepare filament woundcomposites. The epoxy sizing compositions of this invention protect thefibers from abrasion during the filament winding process. The sizing ofthe fiber also permits a smoother delivery of the carbon fiber during.the filament winding. In another common method, the reinforced compositestructure can be prepared by incorporating chopped sized carbon fibersinto the matrix resin and then forming the composite structure, forexample, by press molding.

Since the sizing compositions of this invention are based on epoxidecompounds, carbon fibers sized therewith are compatible with and do notinterfere with adhesion between the carbon fibers and the epoxyresin-hardener systems used as the matrix resin of the composite. Thisis especially true when both the size composition and the matrix resinare both based on diglycidyl ethers of bisphenol A.

The following examples will illustrate the sizing of carbon fibers usingthe sizing compositions of this invention and the preparation ofcomposites using said sized fibers. 1n the examples, partsand'percentages are by weight unless otherwise specified.

EXAMPLES l-9 Commercially available surface treated graphite fiber wassized with epoxy compounds in accordance with this invention in asuitable application process. The particular size and applicationsolvent used in each example are shown in Table 1. In each case thefiber was sized by drawing the fiber through a heated tube and sizingbath as shown in the drawing. The fiber was pulled through the sizesolution at a rate of 2-4 feet per minute. The take-up was a typicalLeesona take-up driver with a motor. The size produced on the fiberranged from soft to hard, as determined by the hand or feel of theresulting sized fiber. The term soft" is used to describe a sized fiberwhich retains its limp hand and the term hard applies to a sized fiberhaving a stiff hand.

Table 1 (Carbon Fiber Sizes) Concentration size Based Size in on theWeight Example Size Solvent Solution) of the Fiber Remarks 1 76%Compound A Diacetone 1.5 1.6 Hard size 24% Compound B alcohol 1 2 76%Compound A 1.1 1.0

24% Compound 8 3 74.7% Compound A 1.1 1.0

23.6% Compound B 1.7% Compound C 4 74.7% Compound A 1.5 1.6

23.6% Compound B 1.7% Compound C 5 37.5% Compound A 1.0 1.0 Medium soft62.5% Compound B size 6 36.9% Compound A 1.0 0.9

61.4% Compound B 1.7% Compound C I 7 Compound D Cl-l,Cl 1.05 1.0 Softsize 8 Mixture E Ethylene 1.0 1.4

9 Compound B Compound A diglycidyl ether of bisphenol A Compound Bdiglycidyl ether of bisphenol A having a molecular weight Compound C Theamide of pelargonic acid.

1 Table l-continued (Carbon Fiber Sizes) Concentration size Based Sizein on the Weight Solvent Solution) of the Fiber H Remarks Example SizeCompound o= 2,6-diglycidyl phenyl glycidyl ether.

Mixture E a mixture of 35% by wt. of bis-2,3-epoxycyclopentyl ether and65% by wt. of the diglycidyl ether of bisphenol A; commerciallyavailable as ERLA 2256 from Union Carbide Corp.

EXAMPLE The carbon fibers sized as describe d in Examples 1-9 were usedto prepare composites employing each of the following epoxy matrixresin-hardener systems:

1. A matrix resin-hardener systemco'mprising 100 parts by weight of2,6-diglycidyl phenyl glycidyl ether (see footnote D of Table 1) andparts by weight of a hardener comprising a eutectic mixture ofmetaphenylene diamine and methylene dianiline. A

Table 2 Resin Matrix- NOL Ring Composites: lnterlaminar Shear StrengthUsing Sized Carbon Fibers Size on Fiber, lnterlaminar Shear StrengthHardener I Curing Sized Based on Wt. of (p.s.i.) v

System Conditions Fiber Y the Fiber Dry Wet* l I 16 hours at .l 10CUnsized 12,500

H followed by' Ex. 1 1.6 14,000 .l1,600 4 hours at 145C. Ex. 2 1.013,600 y r 1 "Ex.3 1.0 1 13,400

Ex. 5 1.0 13,400 r 10,800, EX. 6 0.9 13,400 Ex. 7 1.0 12,000 2 1 hour at125C. Unsized 14,000

followed by Ex. 1 1.6 14,100 12,100 4 hours at 175C. Ex. 2 1.0 13,000Ex. 3 1.0 13,900 EX. 4 1.6 12,800 EX. 5 1.0 12,100 11,100 Ex. 6 0.911,900 Ex. 8 1.4 13,100 3 2 hours at 125C. Unsized 12.700 followed byEx. 9 1.4 12,600 4 hours at 160C.

'Aflfl 12 hour boil in distilled water.

2. A matrix resin-hardener system comprising 100 EXAMPLE 1 1 parts byweight of a mixture of by weight of bis- 2,3-epoxycyclopentyl ether and65% by weight of the diglycidyl ether of bisphenol A (see footnote E ofTable l) and 29 parts by weight of a hardener comprising a eutecticmixture of metaphenylene diamine and methylene dianiline.

"Eutectic mixture of metaphenylene diamine and methylene dianiline;commercially available as Tonox 6040 from Uniroyal, Inc.

3. A matrix resin-hardener system comprising 100 parts by weight ofN,N,N-tris(epoxypropyl)-p,p'- diaminophenyl methane and 49 parts byweight of the hardener 4,4-diaminodiphenyl sulfone.

The composite specimens were made in the form of an NOL ring containingabout 60% by volume of sized carbon fiber. In preparation of thecomposite the carbon fiber is passed through the epoxy resin system,through a tensioning device and onto a rotating mold. The whole systemis enclosed in a vacuum chamber to provide a low void compositespecimen. The mold is removed from the NOL winding device and placed ina curing oven to cure the resin. The time and temperature of curing eachof the resin matrix-hardener systems is shown in Table 2. A discussionof NOL ring specimens and their manufacture may be found inPlasticsTechnology, November 1958, pp. 1017-1024, and

Carbon fibers sized with soft, medium soft, and hard sizes as describedin Example 1-9 were tested for abra sion resistance. A typical filamentwinding delivery system was set up to assess the effect on size on theabrasion resistance of carbon fiber during filament winding. The systemconsisted of a CTC Tensioner, commercially available from CompensatingTension Controls, Inc., set at 3 pounds tension. The fiber was takenover an aluminum wheel, a carbon wheel, and onto a 2.6 inch diametermandrel on a filament winding machine. The degree of abrasion wasmeasured by percent retention of original carbon fiber tensile strength.The results, shown in Table 3, show the improvement in abrasionresistance of carbon fibers when sized with the epoxy size compositions.

Table 3 Abrasion Resistance of Sized and Unsized Carbon Fibers TensileStrength Retention after The preferred sizing compositions of thisinvention are selected from the group oonsisting of (a) a liquiddiglycidyl ether of bisphenol A having a molecular weight of about 340to about 380; (b) a mixture of a solid diglycidyl ether of bisphenol Ahaving a molecular weight of about 380 to 1400 and a liquid diglycidylether of bisphenol A having a molecular weight of about 340 to about380; (c) a mixture of bis-2,3-epoxycyclopentyl ether and the diglycidylether of bisphenol A; and (d) 2,6-diglycidyl phenyl glycidyl ether. Theapplication of the different sizing compositions produce a differentfeel or hand on the fiber ranging from soft to hard. For example, a softsize is obtained when the fiber is treated with 2,6-diglycidyl phenylglycidyl ether, the diglycidyl ether of bisphenol A having a molecularweight in the range of 340 to about 380 or a eutectic mixture of 35% byweight of bis-2,3-epoxycyclopentyl ether and 65% by weight of thediglycidyl ether of bisphenol A. A hard size is obtained when the fiberis treated with a mixture of about 50 to about 80% by weight, preferably76% by weight of the solid diglycidyl ether of bisphenol A having amolecular weight of about 380 to about i400 and from about 20 to about50% by weight, preferably 24% by weight of the liquid diglycidyl etherbisphenol A having a molecular weight in the range of about 340 to about380. A medium soft size is obtained when the carbon fiber is treatedwith a mixture of about 20 to about 50% by weight, preferably 37.5% byweight of the solid diglycidyl ether of bisphenol A having a molecularweight of about 380 to 1400 and about 50 to about 80% by weight,preferably 62.5% by weight of the liquid diglycidyl ether of bisphenol Ahaving a molecular weight in the range of about 340 to 380.

What I claim and desire to protect by Letters Patent l. A carbon fiberhaving coated on the surface thereof from about 0.4 to about 5.0% byweight, based on the weight of the fiber of a sizing compositionselected from the group consisting of polyglycidyl ethers,cycloaliphatic polyepoxides and mixtures thereof.

2. A carbon fiber as set forth in claim 1 wherein the sizing compositionis selected from the group consisting of:

a. a liquid diglycidyl ether of bisphenol A;

b. 2,6-diglycidyl phenyl glycidyl ether;

c. a mixture of a solid diglycidyl ether of bisphenol A and a liquiddiglycidyl ether of bisphenol A; and

d. a mixture of bis-2,3-epoxycyclopentyl' ether and the diglycidyl etherof bisphenol A.

3. A carbon fiber as set forth in claim 1 wherein the sizing compositioncomprises a mixture of about 50 to about by weight of a solid diglycidylether of bisphenol A having a molecular weight of about 380 to about1400 and about 20 to about 50% by weight of a liquid diglycidyl ether ofbisphenol A having a molecular weight of about 340 to about 380.

4. A carbon fiber as set forth in claim 1 wherein the sizing compositioncomprises a mixture of about 20 to about 50% by weight of a soliddiglycidyl ether of bisphenol A having a molecular weight of about 380to about 1400 and about 50 to about 80% by weight of a liquid diglycidylether of bisphenol A having a molecular weight of about 340 to about380.

1. A CARBON FIBBER HAVING COATED ON THE SURFACE THEREOF FROM ABOUT 0.4TO ABOUT 5.0% BY WEIGHT, BASED ON THE WEIGHT OF THE FIBER OF A SIZINGCOMPOSITION SELECTED FROM THE GROUP CONSISTING OF POLYGLCIDY ETHERS,CYCLOALIPHATIC POLYOXIDES AND MIXTURES THEREOF.
 2. A carbon fiber as setforth in claim 1 wherein the sizing composition is selected from thegroup consisting of: a. a liquid diglycidyl ether of bisphenol A; b.2,6-diglycidyl phenyl glycidyl ether; c. a mixture of a solid diglycidylether of bisphenol A and a liquid diglycidyl ether of bisphenol A; andd. a mixture of bis-2,3-epoxycyclopentyl ether and the diglycidyl etherof bisphenol A.
 3. A carbon fiber as set forth in claim 1 wherein thesizing composition comprises a mixture of about 50 to about 80% byweight of a solid diglycidyl ether of bisphenol A having a molecularweight of about 380 to about 1400 and about 20 to about 50% by weight ofa liquid diglycidyl ether of bisphenol A having a molecular weight ofabout 340 to about
 380. 4. A carbon fiber as set forth in claim 1wherein the sizing composition comprises a mixture of about 20 to about50% by weight of a solid diglycidyl ether of bisphenol A having amolecular weight of about 380 to about 1400 and about 50 to about 80% byweight of a liquid diglycidyl ether of bisphenol A having a molecularweight of about 340 to about 380.